Remove dead method from NullFailureDetector.
NullFailureDetector is deprecated.
Migrate tests to use of FailureDetectorImpl (NullFailureDetector is deprecated).
Bugfix: Correctly handle empty membership in FailureDetectorImpl.getRandomMember (impacts FD contract).
Fix test failure caused by revision of FailureDetector contract.
Revise FD contract to include support for notifying of state change.
Add isPinned so others can tell what state an FD is in without having to be a listener.
Add the ability to fake a pin for testing purposes.